An evaporator for a vapor compression refrigerant cycle system generally has a plurality of tubes and header tanks communicating with the tubes. The tubes are arranged vertically and the header tanks are connected to the top ends and bottom ends of the tubes. This kind of evaporator is for example disclosed in JP-A-2001-50686.
Incidentally., in a heat exchanger for cooling air, such as the evaporator, moisture condenses on surfaces of the tubes and fins, which are disposed between the tubes. In a case that the tubes are arranged vertically, the condensed water flows downwardly along the tube surfaces. Further, the condensed water is likely to accumulate around the lower position of the heat exchanger.